The present invention concerns thermosetting compositions based on polymers containing acid anhydride groups consisting essentially of a mixture of:
(A) a polymer containing acid anhydride groups,
(B) a molecular sieve being partially loaded with at least one amine
(C) a filler capable of releasing water upon heating at a temperature above the processing temperature of the mixture (A), (B) and (C).
In the above compositions the amine is released from the molecular sieve B by the water of (C) above the dehydration temperature, then the polymer (A) is crosslinked by the amine.
The compositions of the invention can be made by mixing the components (A), (B) and (C) in an extruder or in any mixing apparatus under anhydrous conditions and below the amine-desorption and the dehydration temperature. The resulting mixture is thermoplastic and can be in the form of pellets. These pellets can be further used to make adhesives (hot melt adhesives (HMA)), to insulate electrical cables, to make tubes by extrusion or any object by injection moulding. Then crosslinking is achieved upon heating.
Prior art U.S. Pat. No. 5,792,816 discloses mixtures of polymer (A) and (B) molecular sieve being partially loaded with at least one amine and explains that release of amine for crosslinking of (A) can be achieved either (i) by intrusion of humidity or addition of water or water saturated solids or salts with crystal water either (ii) by warming the compositions to temperatures above the desorption temperature of the amine.
The desorption temperature of ethylene diamine adsorbed in 4A-molsieve is about 175xc2x0 C. In some cases it is not desirable to warm as high as 175xc2x0 C. to crosslink, it is more convenient to use the water desorbed from a filler. By choosing a proper filler this temperature can be adjusted.
The disadvantage of the above prior art is the difficulty to introduce water, saturated solids or salts with crystal water. The only reasonable way is intrusion of humidity.
Hot melt adhesives are enjoying increasing popularity in the bonding filed. They are solventless, and can be handled without pollution problems. In addition, they are suitable for production processes with short cycle times. The original disadvantage of hot melt adhesives, namely the poor bond strength at elevated temperature, has recently been overcome by using as hot melt adhesives reactive systems which when melted, react to provide materials which cannot be melted a second time or can be melted only at a much higher temperature.
On particularly important group of such a reactive hot melt adhesives are the moisture-crosslinking hot melts. Moisture-crosslinking hot melts are generally understood to be solventless adhesives which, after application to a substrate, acquire their ultimate strength and thermal stability under load by subsequent crosslinking by the action of water.
However, one disadvantage of hot melt adhesives which require the presence of water, is that the hardening reaction cannot take place completely, if at all, if the substrates to be bonded are impermeable to water vapor. The substrates could be steel sheets.
In the application of joint sealing compounds which post-crosslink in the presence of moisture, inadequate hardening or unsatisfactorily long hardening times are obtained when the joints to be sealed are bounded by substrates impermeable to water vapor.
The composition of the invention enable substrates impermeable to water vapor to be satisfactorily bonded with hot melts which post-crosslink in the presence of moisture.
Inventors have discovered that a filler capable of releasing water could be present in the composition.
The curing conditions of the present compositions are substantially independent of the ambient moisture conditions.
Depending on the filler, the present compositions are particularly suitable to make flame retarded insulating sheathings for electrical cables or floor coverings.
According to an advantageous embodiment of the invention the amine loaded molecular sieve (B) is dispersed in a nonreactive polymer (B1) and stored as a master batch under anhydrous conditions.
According to another advantageous embodiment of the invention the composition contains (D) a sufficient amount, typically 1 to 5%, of an unloaded molecular sieve to control the water content of the composition during storage of the masterbatch.
According to another advantageous embodiment of the invention the composition contains (E) a sufficient amount of a monofunctional acid anhydride compound to control the amine content of the composition and prevent preliminary crosslinking. The concentration of the monoanhydride is 0.5 to 10, preferably 2 to 5 equivalent percent of the content of anhydride groups in the polymers.
The addition of the stabilizers (D) and (E) prevents any of odor of amine and uncontrolled release.
The polymer (A) forming the reactive base of these compositions are solid or liquid polymers containing acid anhydride groups with molecular weights Mn of 500 to 1 000 000 Dalton. Polymers with a molecular weight Mn of 1000 to 500 000 Dalton are preferred. The polymers or oligomers contain at least 2 acid anhydride groups and have an acid number corresponding to the acid anhydride groups (determined with water-free alcoholic potassium hydroxide solution according to DIN 53 402) of 0.4 to 445 mg KOH/g. For example, this corresponds to a content of approximately 0.07 to 77 percent of weight of maleic acid anhydride, based on the weight of the functional polymer.
The acid anhydride groups can be distributed over the polymer molecule statistically or regularly or in the terminal position. The introduction of the acid anhydride groups can be achieved by means of copolymerisation, by reaction with terminally located reactive groups, by subsequent addition of unsaturated acid anhydrides onto individual or conjugated double bonds, or by means of graft reactions. The corresponding methods of synthesis are state of the art and disclosed in patent documents and the professional literature. A comprehensive overview of polymers containing acid anhydrides, their methods of synthesis and properties, and especially those which are synthesized using maleic acid anhydride, is contained in B. C. Trivedi and B. M Culbertson: Maleic Anhydride, Plenum Publ., New York (1982).
The polymers used according to the invention are preferably individual, or selected as a blend, from the group copolymers of unsaturated cyclic acid anhydrides, especially maleic or itaconic acid anhydride, with olefinic unsaturated monomers, for examples copolymers of acrylic acid and methacrylic acid esters with maleic and itaconic acid anhydride, addition products of unsaturated cyclic anhydrides on polymers with individual or conjugated double bonds, for example addition products of maleic acid anhydride on double bonds of polybutadienes, addition products of unsaturated cyclic acid anhydrides to styrene-butadiene rubber, thermoplastic styrene-butadiene and styrene-isoprene-block copolymers or to unsaturated decomposition products of high molecular weight natural rubbers, addition products of maleic acid anhydride on partially hydrogenated block copolymers of styrene-butadiene (e.g. SEBS), addition products of unsaturated cyclic acid anhydrides with polymers with mercaptan groups, for examples with an isocyanate prepolymer based urethane of mercaptoethanol, addition products which have been obtained by graft reactions of olefinic unsaturated cyclic acid anhydrides to polymers, for example graft products of maleic acid anhydride to a copolymer of ethylene with vinyl acetate or to a copolymer of ethylene, propylene and butene, polymeric ester-anhydrides or amine-anhydrides obtained through condensation of hydroxy- or aminofunctional polymers with trimellitic acid anhydride, pyromellitic acid anhydride, benzene-tetracarboxylic acid anhydride, benzophenone-tetracarboxylic acid anhydride or ethylene-bis-trimellitic acid anhydride.
The acid anhydride groups can be contained only in one of the polymer components. In many cases blends of polymers with different content of anhydride groups or different range of molecular weights are advantageously used. For example, it can be of advantage to compound a high molecular weight polymer with a low content of acid anhydride groups with a short-chain polymer with a high content of acid anhydride groups.
Advantageously the polymer (A) is a copolymer or ethylene -alkyl (meth)acrylatexe2x80x94maleic anhydride containing by weight 0.5 to 5% maleic anhydride and at least 50% ethylene, preferably at least 60%.
MFI (Melt Flow Index) ranges from 1 to 2000 (190xc2x0 C.xe2x80x942.16 kg).
Melting temperature is advantageously in the range 80-120xc2x0 C.
The alkyl group of the alkyl (meth)acrylate which forms part of the copolymer (A) has up to 24 carbon atoms and can be linear, branched or cyclic. Mention may especially be made, as illustration of the alkyl (meth)acrylate, of n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate or ethyl methacrylate. Among these (meth)acrylates, ethyl acrylate, n-butyl acrylate, methyl methacrylate and 2 ethylhexyl acrylate are preferred.
Molecular sieves of (B) are synthetically manufactured crystalline metal aluminosilicates that belong to the class of minerals known as zeolites. The dehydrated crystals form a network of hollow spaces interconnected by defined capillaries that leads to a large internal surface. They are capable of adsorbing polar chemicals on their crystal structure, respectively their internal surface.
The zeolites used according to the invention are alkali metal aluminosilicates or alkaline earth metal aluminosilicates, and possess a very large number of pores with uniform dimensions. Molecules that are sufficiently small can penetrate into the pores of the anhydrous molecular sieve, and become adsorbed. The pores have regular diameters that, depending on the composition of the zeolite and the temperature, can be between 0.3 and 1.5 nm. For the crosslinking agent according to the invention, commercially available molecular sieve powders are preferred, mainly those with a pore diameter of 0.38 nm (standard commercial designation: type 4A), 0.44 nm (type 5A) and 0.8 nm or 0.84 nm (types 10xc3x97 or 13xc3x97) and marketed by various manufacturers. Free-flowing powder with particle sizes of less than 50 xcexcm, and particularly less than 20 xcexcm, are preferred.
Depending on type, and in a state of equilibrium, the adsorption capacity of the molecular sieve powder for water at room temperature amounts from 20 to 34 percent by weight. The anhydrous molecular sieve powders can be loaded with 3 to 30, preferably with 5 to 25 percent by weight amine.
The loading of molecular sieve powders with polar chemicals is know in the art, and the most common methods are, for example, described by S. Borgmann et al. in Plaste und Kautschuk, 30 (1) 20 (1983).
Depending on the chemical and physical properties of the amines, these are deposited via the gas phase, for example in a current of a carrier gas, via sublimation of the amine and adsorption into the molecular sieve, or via solutions in plasticizers, liquid diluents or solvents. The solvents can be removed after adsorption of the amine by distillation, if necessary under reduced pressure.
The loaded molecular sieves can also be used in a blend with other unloaded molecular sieves serving as desiccants or stabilizing agents. Additional molecular sieves for the adsorption of water can also have other pore diameters.
The use of different amines on one or different molecular sieve powders is also advantageous.
Amines for the crosslinking of polymers containing acid anhydride groups are aliphatic, alicyclic, heterocyclic or aromatic, primary or secondary amines with effective molecular diameters less than 1.5 nm. Di- or polyamines are suitable for crosslinking.
Examples of suitable amines according to the invention are:
Ethylenediamine, propanediamine, butanediamine, pentanediamine, hexanediamine, isomers of the named amines, 1,2- and 1,4-diaminocyclohexane, diethylene-triamine, triethylene-tetramine, tetraethylene-pentamine, N-aminoethyl-3-aminopropyltrialkoxysilane, triamino-functional propyltrialkoxysilane, piperazine, aminoethyl-piperazine, di-aminoethyl-piperazine, xylylenediamine, isophoronediamine, 3,3xe2x80x2-dimethyl-4,4xe2x80x2diaminodicyclohexyl-methane, 4,4xe2x80x2-diaminocyclohexylmethane, 4,4xe2x80x2-diamino-diphenylmethane, 1,4-diamino-benzanilide.
In a particular embodiment of the crosslinking agent according to the invention, up to 50 equivalent percent of the reactive groups of the crosslinking agent can be replaced by hydroxy groups, for example by hydroxy groups of aminoalcohols. Instead of molecular sieves loaded with amines, the molecular sieves loaded with aminoalcohols can be used for crosslinking the polymers containing anhydrides.
Examples of aminoalcohols are ethanolamine, diethanolamine, propanediamine, dipropanolamine, N-hydroxyethyl-aniline.
The molecular sieve powders loaded at least partially with an amine can additionally be loaded with a catalyst for the reaction of the acid anhydride with the hydroxy bonds. Suitable catalysts, which are preferably used in amounts of maximum 2 percent weight related to the total weight of (A) and (B), are preferably tertiary aliphatic amines with 1 to 14 C-atoms in the alkyl substituents, diazabicyclooctane, diazabicycloundecene, dimethylbenzylamine, methylmorpholine, dimethylpiperazine, N-alkyl substituted imidazole and their blends.
Below the dehydration temperature of (C), the loaded molecular sieve of (B) are stable even in the presence of (A) and (C). Depending on the type of (C), release of amine doesn""t occur within 30 minutes, provided the temperature is 10xc2x0 C. below the dehydration temperature of (C) and the desorption temperature of (B). The compounds The compounds are stable several hours at 75xc2x0 C., or a minimum of 2 weeks at room temperature.
Advantageously the molecular sieve loaded with amine is available as a master batch consisting essentially of a polymer (B1) in which the loaded molecular sieve is dispersed.
Once the molecular sieve is loaded it is incorporated in (B1) in the molten state. The master batch is made by any mixing equipment such as an extruder or a branbury mixer. (B1) is any polymer compatible with (A) and having a melting temperature not above 100 or 130xc2x0 C. to be sure that during incorporation of the loaded molecular sieve there is no release of the amine by a high temperature.
The proportion by weight of loaded molecular sieve and (B1) are 10-90 to 50- 50.
Advantageously (B1) is chosen among the polyolefines, the polyalphaolefines and the blocks copolymers SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene) or SEBS (styrene-ethylene butene-styrene).
Preferred (B1) are copolymers of ethylene and alphaolefins, copolymers of ethylene and vinylacetate, copolymers of ethylene and alkyl(meth)acrylate. It is recommended that (B1) has no groups reactive with the amines. Alkyl(meth)acrylate may be chosen among the alkyl (meth)acrylates already cited for (A).
Preferred (B1) have MFI between 2 and 1500 (190xc2x0 C.xe2x80x942.16 kg).
The stochiometric relationship of the acid anhydride groups of the polymer (A) to primary or secondary amino groups of the crosslinking agent (B) lies in the range between 0.5 and 5, preferably between 0.6 and 3.
Under anhydrous conditions, blends (B) of molecular sieves loaded with amines and polymers (A) containing acid anhydride groups are stable.
Release of the amines adsorbed in the molecular sieve is by means of water and/or by warming. Water is generated by (C).
Alternatively, the adsorbed amines can be released by warming of the compositions to temperatures above the desorption temperature. At temperatures above the so-called desorption temperature, the adsorption equilibrium will be on the side of the free amine.
Loaded with ethylenediamine, molecular sieve powders of type A4, having a desorption temperature of 175xc2x0 C., are particularly stable when mixed with polymers containing acid anhydride groups. Because of the low equivalent weight of the ethylenediamine and the low cost of the molecular sieve powder of type 4A, the use of this combination is also economically advantageous.
For example, on the basis of experiments, the following temperatures have been established, the measured desorption temperature depending on the heating rate of the system:
The equilibrium can be shifted in the direction of the free amine, and the crosslinking thus initiated or accelerated, by heating the system, and also by means of the release water from (C).
Heating of the system to crosslinking temperature can ensue by means of radiated heat, convection heat, by means of resistance, induction or microwave heating, by frictional heat or with ultrasonic vibrations.
The filler (C) is a solid or a powder releasing water upon heating. Generally (C) has no melting point, it is mixed with (A) and (B) by any means such as an extruder, a mixer or any means. (A) and (B) are in a molten state. The temperature at which (A), (B) and (C) are mixed (the processing temperature) is between 75 to 200xc2x0 C., generally between 80 and 130xc2x0 C. The mixture of (A), (B) and (C) is advantageously in the form of pellets.
The man skilled in the art choose (B) to be sure there is no release of amine during the mixing of (A), (B) and (C).
When the composition of the invention [(A)+(B)+(C)] is used as adhesive or tube or any object it is processed (injected . . . ) in the molten state at the same temperature range used to make the pellets. Then crosslinking occurs by heating.
(C) is any substance which release bound water. Both organic and inorganic substances which contain water in physically or chemically bound form and which release it again on heating may be used for the invention.
Suitable fillers for the invention are air-dried oxides, hydroxides or salts containing water of crystallization of the alkali metals, alkaline earth metals and metals of the third main group and also air dried oxides, hydroxides or salts containing water of crystallization of secondary group elements.
Substances which release water of crystallization at a temperature in the range from 80xc2x0 to 180xc2x0 C. and which are readily available in relatively large quantities are preferred materials.
Metals of the third main group comprise metals from Group IIIA and the secondary group elements comprise the elements of Groups, IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIIIB of the PERIODIC CHART OF THE ELEMENTS, MERCK INDEX, TENTH EDITION, Merck and Co., Inc. 1983. Preferred compounds of these groups comprise air dried oxides, hydroxides and salts containing water of crystallization of copper, iron, vanadium, chromium, molybdenum, tungsten, manganese, cobalt, nickel, zinc, cadmium and aluminium.
Particularly preferred metal salts containing water of crystallization useful in the invention are iron sulfate (FeSO4xc3x977H2O), barium hydroxide (Ba(OH)2xc3x978H2O), calcium sulfate (CaSO4xc3x972H2O), copper sulfate (CuSO4xc3x975H2O), magnesium phosphate ((Mg)3(PO4)2xc3x974H2O), sodium silicate (Na2SiO3xc3x979H2O), copper acetate (Cu(CH3COO)2xc3x972H2O), sodium silicate (Na2SiO3xc3x9712H2O), sodium phosphate (Na3PO4xc3x9713H2O), sodium sulfate (Na2SO4xc3x9710H2O), calcium lactate (Ca(CH3CH(OH)xe2x80x94COO)2xc3x975H2O), aluminum trihydrate (Al2O3xc3x973H2O), as well as magnesium hydroxide Mg(OH)2 and zinc hydroxide Zn(OH)2. Properties of some metal salts containing water are as follows:
Filler (C) could be a substance which release water other than crystal or dehydration water: Boric acid H3BO3 at 169xc2x0 C. gives H2O and HBO2.
Another class of fillers (C) which are useful in the invention are inorganic compounds which form structures containing voids or passages in which water is bound or incorporated at room temperature and which release the bound or incorporated water above room temperature or in vacuum. Examples of preferred substances are zeolites which are normally used as ion exchanger materials or molecular sieves. Within this group, zeolite A powder are particularly preferred.
It would not be departing from the scope of the invention to use a mixture of different fillers (C) or different kind of fillers (C).
Advantageously (D) are 3A or 4A molecular sieve.
Advantageously (E) is maleic anhydride or tetrahydrophtalanhydride.
The amount of water released which is required to release the amine of (B) and finally crosslink (A) is about in weight ⅓ to xc2xd of the introduced amine weight.
The crosslinking temperature is influenced by the type of molecular sieve, by the amine, by the concentration of the amine adsorbed on the molecular sieve, and the filler (C).
The crosslinking temperature can be adjusted with the type of (B) and (C) and is typically in the range of 90 to 200xc2x0 C.
The processing temperature is in the range of 75 to 200xc2x0 C. and depends on the equipment and the specific process used: The process temperature is 1) below or 2) equal or above the dehydration temperature of (C)
1) If the process temperature is below the dehydration temperature of (C), a stable uncrosslinked compound of the polymer (A), the amine-loaded molsieve (B) and the water containing filler (C) is produced first. It will crosslink in a second step when exposed to temperatures above the dehydration temperature of (C).
2) In a another procedure, the polymer (A) and the amine-loaded molecular sieve (B), or a masterbatch containing (B), are blended at a temperature above the dehydration temperature of (C). The water releasing filler (C) is added to the blend of (A) and (B) immediately before extruding the blend. After extrusion, the released water will diffuse and penetrate the amine-loaded molsieve, desorb the amine, which crosslinks the reactive groups of the polymer.
This second procedure lends itself to the use of an extruder with different temperature zones. For example, the polymer (A) is kneaded and molten in the first zone at a temperature of 120xc2x0 C. In the second zone at a temperature of 130xc2x0 C. the loaded molecular sieve (B), with an amine desorption temperature of 175xc2x0 C., is introduced and blended with the polymer (A). Finally before extruding the blend of (A)and (B), a water generating compound, with a dehydration temperature below 130xc2x0, is added in the third zone at 150xc2x0 C., blended and immediately extruded. The blend, extruded on an electrical wire, will spontaneously crosslink within a few hours or days, showing no creep at 180xc2x0 C.
The properties of the uncrosslinked and crosslinked compositions can be specifically controlled by those skilled in the art and depend, amongst other factors, on the polymer content, on the anhydride content of the polymer, on the degree of polymerization, on the proportion of comonomers, on the functionality, on the ratio of acid anhydride groups to the functional groups of the crosslinking agent, and the type of functional groups, and filler (C).
The compositions of the invention may contain additives such as pigments, powdered metal, dyestuffs, carbon black, pyrogenic silica, short-chopped fibers, powdered rubber, plasticizers, extender oils, bitumen, non-reactive polymers, resins, tackifying resins, adhesive additives, surfactants, silicone oils, flame retarding additives, antioxidants and light stabilizers, anti-corrosion agents, scents, fungistatic and bacteriostatic agents, thixotropic agents, blowing agents and foam stabilizers and solvents. The use and effect of these additives and their preferred concentrations are state of the art and known to the expert in the art.
The compositions according to the invention are suitable as reactive hot melt adhesives which are stored under water-free conditions, and later are applied thermoplastically in a molten state. By heating, (C) releases water and the hot melt crosslinks. After cooling, they will solidify to a composition with improved mechanical strength, heat resistance and resistance to solvents.
The present invention concerns also the hot melts comprising the compositions (A), (B), (C) hereabove. The present inventions concerns also shaped articles of manufacture comprising a composition (A), (B), (C) as describe hereabove.
The compositions of the present invention are suitable to make coverings having a good resistance to wear abrasion and scratching such as floor coverings. The compositions of the invention are suitable for flame retardant compositions.
The present invention relates to flame-retardant polymer compositions. More especially, these compositions do not contain halogenated derivatives and are capable of being processed by conventional techniques into articles having good fire resistance, such as, in particular, insulating sheathings for electrical cables.
Improvement of the fire resistance of compositions containing polymer materials is a constant objective of the manufacturers and processors of these materials, directed towards obtaining a significant reduction in the flammability and capacity for flame propagation of these materials. The use of halogenated derivatives as flame-retardant agents is well known, but has the great drawback of leading, on combustion, to toxic and corrosive gases. The manufacturers and processors have hence turned their attention to the development of compositions containing oxides, hydroxides or inorganic salts of metals, such as hydrated alumina and magnesium hydroxide.
However, the addition of such inorganic fillers in a sufficient amount to obtain good fire resistance leads to materials having mediocre mechanical properties and/or presenting great difficulties of processing by conventional methods such as extrusion.
The compositions of the invention in which (C) is Al2O3xc3x973H2O or Mg(OH)2 have better properties due to the crosslinking, in particular there is no creep.
The composition according to the invention generally have a limiting oxygen index (as defined below) of at least 30%, an elongation at break of at least 100% and a rupture strength of at least 10 MPa.
The compositions according to the invention may be prepared by kneading the ingredients in powder or granule form so as to obtain a homogeneous, ready-to-use mixture.
They may also be prepared by kneading and then melting and granulation of the constituents followed by extrusion and granulation. The extrusion may also be carried out on a co-extruder; the compositions in which the polymer phase is in the molten state and the hydrated inorganic filler regularly dispersed may then be processed directly, for example into sheathing for metal cables.
A second aspect of the present invention relates to industrial articles comprising a composition as described above. More especially, these industrial articles are sheathings for electrical cable.
Once the compositions are shaped into cable sheathings a heating or water diffusion with time achieve the crosslinking.
The proportions of (A), (B) and (C) may be (by weight) respectively 30 to 60/5 to 10/35 to 65, (C) may be only Al2O3xc3x973H2O and/or Mg(OH)2 or a mixture of Al2O3xc3x973H2O and/or Mg(OH)2 with another filler to release more water, said other filler being for example a partially water loaded zeolite, or CaSO4xc3x972H2O.
The present invention concerns also an electrical cable comprising a sheathing, said sheathing comprising a composition (A), (B), (C) of hereabove.
A part from this application in cable manufacture, the compositions according to the invention find other applications in which their character of fire resistance and their good mechanical properties are required. They have the advantage that they can be processed in industrial articles (sheets, plates, profiles, hollow bodies, tubes, pipes) having improved fire resistance, by the conventional techniques for processing polyolefins (extrusion, injection, rotational molding).